This invention relates generally to the fields of polymer and pyridine chemistry, and more specifically to new compositions of matter comprising N-substituted polyvinylpiperidines and to an efficient, high-yielding process for their preparation.
Pyridine, with its characteristic aromatic ring structure, much like benzene, is the parent ring system to a large number of substituted homologues and derivatives having uses both in naturally occurring products and valuable industrial, pharmaceutical and agricultural chemicals. Piperidine, being one such derivative with the formula C.sub.5 H.sub.11 N, is a completely saturated ring compound recognized for its strong basicity and solubility in solvents such as water, alcohol and benzene. Common uses reported for piperidines are many and varied, including solvents and intermediates, curing agents for rubber and epoxy resins, catalysts for condensation reactions, and ingredients and oils in fuels and the complexing agents. Substantial work, both in industry and in academia, has been done with pyridines, piperidines and related compounds over the years. One aspect of this work has involved the use of pyridines as bases for synthesis of polymeric materials. In this regard, poly-2 and poly-4 vinylpyridine have been commercialized as valuable vinyl-type polymers for such uses as photographic dye mordants, tablet coating materials, and various uses in the textile and paper industries. These substances are marketed as linear and as cross-linked polymers and exhibit differing properties, such as their respective solubility and insolubility in organic solvents such as water, isopropyl alcohol and aqueous mineral acid. These substances also show up in copolymer structures as with styrenes.
One might expect polymer chemistry to have advanced in like fashion with piperidine-base materials. However, this is not the case. Although 2- and 3-vinylpiperidine have been reported synthesized in monomeric form, for example, poor yields, if any, have been reported in attempts to prepare their polymeric counterparts. A. Ladenberg, Ber., 22, 2583 (1889); A. Ladenberg, Ann., 301, 129 (1898); R. Merchant, C. S. Marvel, J. Am. Chem. Soc., 50, 1197 (1928); H. A. Iddles, E. H. Lang, D. C. Gregg, ibid., 59, 1945 (1937). Applicants have also encountered problems with their attempts to directly prepare and polymerize these monomers.
Only one reference is known to applicants which suggests an alternate synthesis of these polyvinylpiperidines. That reference is A. Katchalsky, K. Rosenheck, B. Altmann, J. Polymer Sci., vol. XXII, pp. 955-965 (1957). It suggests hydrogenating either poly-2-vinyl- or poly-4-vinylpyridine in solution in glacial acetic acid using 5% palladium on charcoal as a catalyst. Full reduction was reported after 20 hours of hydrogenation at an initial hydrogen pressure of about 3,500 p.s.i. and at a temperature of 220.degree.-250.degree. C. In applicants' efforts to reproduce these results, applicants found the reaction conditions of the reference to be so harsh as to be barely susceptible of laboratory testing, and doubtful that the process would have any commercial application. In attempting to hydrogenate using the reference procedure under conditions of up to 200.degree. C., initial hydrogen pressures of up to 2,000 p.s.i.g. and reaction periods up to 12 hours, applicants were only able to evidence a maximum of about 50-60% hydrogenation. This is an unacceptable percentage for commercial application as the differing characteristics of both the starting pyridine and ending piperidine polymers will be present in the reaction product. Moreover, the corrosive atmosphere created by the use of acetic or any acid under these conditions causes a hazardous environment, both for workers and for equipment, significantly undercutting any commercial potential for the process. In addition, even if the reference procedure is enabling at its more harsh conditions not tried by applicants, the reference itself reports significant degradation of the polymers causing substantial reductions in molecular weights in all but the very smallest starting materials.
Aside from this Katchalsky et al. reference which was published in 1957, applicants are aware of no publication reporting synthesis of these or other polyvinylpiperidines or teaching a procedure for their preparation. Applicants are also aware of no commercial use or availability of these polymers. Nonetheless, the need for such strong bases in polymeric form has continued to increase, and exists today. If available, substituted forms of these polymers would also have existing and potential uses both as intermediates and as end products for use with epoxy resins, urethane foams and others.